Microspeakers are classified into inner ring magnet type, outer ring magnet type, inner and outer ring magnet type, and bar magnet type depending on the structure of a magnetic circuit.
FIG. 1 is a view showing a magnetic circuit structure for a conventional inner ring magnet type microspeaker. A magnet 22 is installed on a yoke 21, and a plate 23 is attached to the top of the magnet 22. The magnet 22 is a magnetic circuit which is located inside a voice coil 30 and forms a magnetic path through the yoke 21 and the magnet 22 by folding up the yoke 21 outside the voice coil 30.
FIG. 2 is a view showing a suspension bonding structure for the conventional inner ring magnet type microspeaker. A diaphragm and a protector are omitted in order to clearly show the structure of a suspension 50. The aforementioned magnetic circuit is installed in a frame 10, and the voice coil 30 and the suspension 50, which guides a vibrating body such as a diaphragm to vibrate only vertically without causing partial vibration and abnormal vibration, are seated on the frame 10. The voice coil 30 can be attached to the bottom of the suspension 50, and the diaphragm can be attached selectively to the top or bottom of the suspension 50.
FIG. 3 is a view showing a suspension provided in the conventional inner ring magnet type microspeaker. Referring to FIGS. 2 and 3, the suspension 50 is installed on the frame 10, and includes an outer peripheral portion 51 serving as a substantially rectangular ring-shaped seating end, a substantially rectangular ring-shaped inner peripheral portion 52 located within the outer peripheral portion 51, spaced apart from the outer peripheral portion 51, and a connecting portion 53 that connects the inner peripheral portion 52 and the outer peripheral portion 51 and elastically supports the inner peripheral portion 52. In addition, if necessary, the suspension 50 is formed of a conductive material or FPCB. In this case, the suspension 50 includes a first land portion 54 for connecting to the lead wire of the voice coil 30 and a second land portion 55 for connecting to a terminal 70 installed on the frame 10.
With this suspension structure, the outer periphery of a ring-shaped side diaphragm (not shown), which is seated on the frame 10 and has a predetermined width, is attached to the outer peripheral portion 51, and the inner periphery of the side diaphragm (not shown), the outer periphery of a center diaphragm (not shown), and the voice coil 30 are attached to the inner peripheral portion 52. Referring to the magnetic circuit of FIG. 1, the voice coil 30 should be located in an air gap between the magnet 22 and the folded-up portion of the yoke 21. Accordingly, although the magnet 22 is smaller in size than the inner peripheral portion 52 of the suspension 50, the size of the frame 10, i.e., the overall size of the microspeaker, should be at least equal to or larger than the size of the outer peripheral portion 51 of the suspension 50. Hence, the size of the magnet 22 is limited by the shape of the suspension 50 even if the microspeaker is large in size.